In an LDI apparatus, CAD data used for designing a circuit pattern are converted into vector data format, and then contours are calculated from the vector data. After that, the contours are further converted into raster data for imaging. From the raster data, ON and OFF pixels for a laser beam are obtained. The ON pixels are irradiated with the laser beam.
FIG. 7 is a view showing a configuration of background-art LDI apparatus.
A laser source 1 is mounted on an optical table 16. The optical table 16 is disposed on a column 17 on a bed 18. A laser beam 5 emitted from the laser source 1 enters an acousto-optic modulator (hereinafter referred to as “AOM”) 4 reflected by mirrors 2 and an expander 3. A laser beam 5a modulated by the AOM 4 is deflected by a polygon mirror 6 and enters an fθ lens 7. The laser beam 5a emerged from the fθ lens 7 is deflected toward the downward direction of FIG. 7 by a reflection mirror 8, and enters a cylindrical lens 9. The laser beam 5a emerged from the cylindrical lens 9 is incident on a workpiece 10. A dry film resist (hereinafter referred to as “DFR”), a photo-resist or the like on the workpiece 10 is exposed to the laser beam 5a. On this occasion, a table 12 where the workpiece 10 is mounted moves in a sub-scanning direction (Y-axis direction in FIG. 7) at a constant speed. A linear motor 14 moves the table 12. A pair of guides 13 guide the table 12. A camera 60 is disposed above the table 12. The camera 60 is mounted on a not-shown shifter by which the camera 60 can be positioned desirably in the X-axis direction. The camera 60 is connected to a not-shown image processor. For example, in order to determine an imaging position, the camera 60 is used for picking up images of alignment marks disposed in the surface of the workpiece 10 (Patent Document 1).
FIGS. 8A and 8B are views showing the position of a start sensor. FIG. 8A is a view in the X-axis direction of FIG. 7, and FIG. 8B is a view in the Y-axis direction of FIG. 7.
A mirror 11 is disposed under the left end portion of the cylindrical lens 9 in FIG. 7. A start sensor 15 is disposed in the direction of reflected laser beam from the mirror 11. In order to align the scanning start points of rows, which mean the rows of the exposed pixels by the main scanning (X-axis direction), imaging in each scan in the main scanning direction is started when a predetermined time has passed after the start sensor 15 has detected the laser beam 5a reflected by the mirror 11 (the distance between the detection position and the imaging start position is 10 mm in the illustrated case). Thus, the scanning start points of rows are aligned.
To machine a printed circuit board, xy coordinate axes are determined with reference to alignment marks provided in the surface of the printed circuit board (workpiece) in advance before machining. It is difficult to fix the printed circuit board onto the table so that the xy coordinate axes are set in parallel with the XY coordinate axes of the driving system of the LDI apparatus. Therefore, a not-shown rotating mechanism is provided in the table 12. By the rotating mechanism, the workpiece 10 is rotated so that the xy coordinate axes of the workpiece 10 can be set in parallel with the XY coordinate axes of the driving system of the LDI apparatus.
There are various methods for manufacturing so-called multilayer boards. In a pin lamination method or a mass lamination method, double-sided boards each having conductor layers disposed on the both sides of an insulating layer are laminated to one another with insulating layers interposed. In order to improve the reliability of such a multilayer board as a product, it is necessary to precisely position patterns to be disposed on front and back surfaces of each double-sided board.
When a photosensitive material such as resist is applied to surfaces of conductor layers of each double-sided board, the following technique can be used (Patent Document 1). That is, an exposure unit is provided on the back surface side. When the front surface side is being exposed to light, exposure is performed on the back surface side so as to form an alignment mark thereon. When the back surface side is exposed to light, the back surface side is machined based on the position of the alignment mark formed by the exposure in advance, as described above. According to this technique, a pattern to be disposed on the back surface side can be determined precisely with respect to a pattern disposed on the front surface side.
Patent Document 1: WO 02/39794
However, exposure is merely performed but development is not performed in the above-mentioned technique, that is, a latent image is used. Therefore, when some kind of photosensitive material is used, there is a case where the alignment mark cannot be identified. Development on printed circuit boards or partial development only near portions exposed to light in order to identify the alignment mark increases the number of processes of operation. Therefore such a solution cannot be employed.